Protective system



' Aug. 2, 1932. E. a. MALLORY v PROTECTIVE SYSTEM Filed April 23, 1926 WITNESSES: 4 INVENTOR fdward B/Vd/oy.

sn Mhm e BY Patented Aug. 2,1932

UNITED STATES PATENT OFFICE EDWARD IB. HALLOBY, OI TENAFLY, NEW JERSEY, ASSIGNOR TO WESTINGHOUSE ELEC- TRIO & MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA PROTECTIVE sYs'rnn:

Application filed April 23,

My invention relates to systems for indicating the presence of material objects in locations where they are not desired and has particular reference to systems designed to serve as burglar alarms.

' Numerous attempts have been made in the past to devise alarm systems which will give an indication of the presence of intruders in buildings, enclosures, etc., the majority of which have depended upon the displacing of some material object such as a wire, board or the like to give an audible signal.

Other systems have been employed, the operation of which depends upon the making or breaking of an electric circuit which in turn operates relays that control the signalling means. Bank vaults have been pro tected by networks of charged wires placed in locations where they must, of necessity, be broken by any attempt made at entry by unauthorized intruders, the breaking of these wires, in turn causing definite indications at a central oifice.

Other forms of protective systems have been used, such as networks of piping filled with steam or other gas, or liquid, under pressure, explosives imbedded in the vault walls, etc. but none of them have been infallible in giving an alarm.

As a solution of the problem of preventing unlawful ingress into a relatively large area, no system, insofar as I am at present aware, has given entire satisfaction. For example, lumber yards or other places where large amounts of valuable material are stored have always been susceptible to entry by unauthorized persons unless an adequate force of watchmen is maintained.

Such places have, in the past, been surrounded by charged wire fences and the like, or by fences comprising one or morecharged wires, the breaking of which would give an alarm. Such systems have, of course, provided a certain amount of protection, but persons having sufiicient skill and knowledge have always been able to circumvent them.

It is accordingly an object of my invention to provide an alarm system which will give reliable protection against intruders.

1926. Serial No. 104,096.

A further object of my invention is to provlde an alarm system which is applicable to either large or small enclosures.

Another object of my invention is to provlde an alarm system with which it is difiicult to tamper.

Another object is to provide an alarm system which will give an indication of any undesired entry into a protected space irrespectlve of what may be the entering agency, such as flame, smoke, gas, or the like, or material objects.

Another object of my invention is to pro- .vlde an alarm system which will not have to be repaired or re-set after each indication.

A still further object of my invention is to provide an alarm system which does not depend upon physical contact of the intruder with any portion of the system in order to give an indication.

Another and incidental object of my inventi-on is to provide what may be termed a telltale system that will give a reliable indication of the presence of foreign ele ments in enclosures such as boxes, bales, etc. or packages such as cotton bales, tobacco bales, or the like.

In order to provide a system that is equally applicable to either large or small areas I make use of the fact that no matter what object is introduced into a space between two oppositely charged conductors the capacity therebetween will be changed.

In a preferred form of my invention, I employ the space to be protected as the dielectric of a condenser across which is impressed an alternating current. Changes in the dielectric occasioned by the presence therein of undesired agencies cause a re-distribution of the currents carried by circuits associated with the condenser, and this redistribution is utilized in order to give an audible indication.

My invention may take a variety of forms,

depending upon the size of the space to be necessary to provide a plurality of antennae overlying this area and to, utilize these antennae as one plate of the condenser.

In-addition, it is entirely feasible to use this method and a modified form of ap aratus (not shown) for the detect on of oreign articles such as stones, etc., in bales or packages which have been prepared for shipment. At the present time, th s 1s often done by the use of X rays but my invention provldes a much cheaper and an equally reliable method for this pur ose.

For a more comp ete understandin of my invention, reference is made to the fo low ng specification and the drawing accompanying and forming a part thereof.

Figure 1 1s a diagrammatic view of a preferred form of my invention, and

Fig. 2 is a diagrammatic view of a mod1- field form incorporating a balanced network.

Referring specifically to Fig. 1, a thermionic tube 1, provided with the usual grid 2,

late 3 and filament 4, has connected, between its grid and filament, a tuned circuit comprising an inductance 5 and a condenser 6.

.Coupled to the inductance 5 is a second inductance 7 connected to the plate 3. This tube is provided with the usual Abattery 8 and Bbattery 9. In conductive connection with the grid 2 is an extended metal sur-' face 10, which may be an antenna a plate or the like.

A second thermionic tube 11 is provided. having a plate 12, a grid 13 and a filament 14, and between the grid and filament of this tube, is provided a tuned circuit, comprising an inductor 15 and a condenser 16. This grid circuit is further provided with a grid condenser 17 and grid leak 18. Serially included between the plate 12 and the filament 14 is a sound-emitting apparatus 19, a B-battery 20 and an inductor 21 which is coupled to the inductor 15. This tube is provided with an Abattery 22 or it may be energized from battery 8. It is also obvious that the batteries 20 and 9 may be consolidated. The filament 4 is conductively con nected to the ground 23 fora purpose which will be explained.

In the operation of this form of my invention, the thermionic tube 1 is caused to oscillate by the coupling between the inductors 5 and 7 the frequency of this oscillation being controlled by the capacitance existing between element 10 and the ground 23 as well as the value of inductors 5 and 7, and the condenser 6. The thermionic tube 11 is also caused to oscillate at a radio frequency in substantially the same manner, the oscillations being rectified by the action of the condenser 17 and grid leak 18. The frequency of oscillation of the tube 11' is controlled as is well knownin the art, by the values of the condenser 16 and the inductor 15.

The frequencies of these two thermionic tube oscillators are so chosen that the fre' quency of the beat note produced by their interaction in the sound producer 19 is either zero or at a frequency above or below audibility. If, however, the capacitance existing between the element 10 and the ground 23 is chan ed by a change in the dielectric between t ese elements, the frequency of oscillation of tube 1 will be altered, and the con stants of the circuit are so chosen that any change in this frequency will give rise to an audible beat note.

In the practical application of this form of my invention, the dielectric between element 10, which may be a plurality of antennae, a wire netting or the like, and the ground 23 is either coextensive with the space to be protected against intrusion, or is made to comprise said space. When this space is free from the presence of undesired agencies, the sound producing device is silent. When, however, the dielectric constant of the protected space is changed by the ingress or resence of a foreign agency or object, the requency of oscillation of tube 1 is changed sufficiently to give an audible si 'nal.

The sound producer 19 may, of course, be replaced by any desired number of audio frequency amplifiers, the leads from which may be carried to a central station and produce an indication there of the presence of intruders in the space to be protected.

Referring specifically to Fig. 2, a balanced network 25 is provided which, for example,

may take the form of a Wheatstone bridge.

The arms of the bridge may comprise a plurality of variable inductors 26 and 27 and a plurality of variable impedance devices 28 and 29. The impedance devices 28 and 29,

condenser 30, and inductor 26 may be replaced by other suitable forms of impedances,

if desirable. The arm 32 of the bridge com-- prises the space to be protected, which is coextensive With or involves the dielectric between a condenser formed by the element 33 and the ground 23. The element 33 may be either a single antenna, a plurality of electrically connected antennae, a wire netting, a plate or the like. The inductor 27 may be either the self-inductance of the element 33 or may be an extra lumped inductance.

Connected serially in the diagonal of the network between the points 34 and. 35 is the input circuit of a detector device 36 which, for example, may be a thermionic tube provided with a grid 37, a filament 38 and a plate 39. The input circuit of the detector 36 comprises an inductor 40, a condenser 41 shunting the inductor 40, and the usual grid condenser 42 and grid leak 43. A battery 44 is provided as a source of filament current. In the output of the detector 36, serially between the plate 39 and the filament 38 are included the primary of an audio-frequency Coupled to an inductor 51 connected across points 52 and 53 of the network is an oscillation generator 54, which for example, may be a thermionic device 55 having a filament 56, a grid 57 and a plate 58. Connected between the filament 56 and the grid 57 is an inductor 59, and connected between the filament 56 and the plate 58 is included a second inductor 60, a source of potential 62 and a chopper 63. The inductors 59 and 60 are serially connected and are shunted by a tuning condenser 61.

Any other well known form of oscillation generator may be substituted for the Hartley type illustrated, provided it is capable of being accurately adjusted to give oscillations at a definite high or radio frequency, which may be broken up into audio frequency groups by a chopper 63.

In the operation of the form of my invention illustrated in Fig. 2, after the various thermionic tubes have been energized, the network is balanced bv adjusting the various reactances. The element 33 will, of necessity,

have a certain amount of inductance, and this inductance, represented'by element 27 as well as the capacitance across element 33 and the ground 23, is balanced by the variable inductor 26 and variable condenser 29. When perfect balance is attained, there will be no voltage impressed across the input circuit .of the detector device 36 by reason of the oscillation generator 54.

The input circuit 40, 41 is tuned to the frequency of the. oscillations being generated by generator 54, and if the balanceof the bridge is disturbed an oscillating current of this frequency will build up in the resonant circuit 40, 41 and be detected or rectified by device 36. The rectified current will be at an audio frequency inasmuch as the'oscilla tions impressed across the input circuit 40, 41 are broken up by the chopper 63 into groups at an audible frequency. The unbalance of the bridge may be caused by the presence of some foreign element or agency in the space to be protected between the element 33 and the ground 23, and, provided the device is carefully adjusted for maximum sensitivity it is not necessary that the change in the dielectric comprising the protected space be a large one.

This form of my invention lends itself readily to the protection of any desired space. The ground connection may be simply a wire to some convenient grounded point, which in a building might be a radiator, water pipe or the like, while the element 33 may take practically any form desired, as, for example, a singe antqnnaor a metal plate insulated from ground and overlying or bounding the entire protected area. It is conceivable that the space between the element 33 and the ground 23 may be that space comprised in a very large enclosure such as a lumber yard or the li e, and in such case the element 33 would take the form, perhaps, of an umbrella type antenna placed suificiently high above the protected space to be out of the reach of intruders and consequently not easily tampered with.

Again, the element 33 and the ground 23 might be replaced by two opposed metallic surfaces between which an intruder must, of necessity, pass in order togain access to a protected area. It is also feasible to close the circuit between the element 33 and the ground 23 b means of a large loop which loop might e passed around one or more openings such as windows or doors, through which it would be necessary that an unlawful entry be made. In the latter event, there would be inserted in the arm 32 of the net work, a variable condenser to balance the condenser 31.

It is also obvious that the sound producing device 50 may be replaced by an amplifier, the output of which is led to a central station where either a visual or audible indication may be made.

The entire apparatus illustrated in Fig. 2 may be placed in a position inaccessible to intruders such as the top of a radio tower or at a similar location.

It is also, as explained in connection with Fig. 1, feasible to use this form of my invention to detect the presence of foreign articles in closed packages, bales or the like, in which event the element 33 and the ground 23 would be replaced by spaced electrodes between which the article to be tested would be passed. The system would be so adjusted that properly packed articles would give little or no indication in the sound producing element 50 while the presence of foreign materials would so disturb the dielectric constant of the space between the spaced electrodes that a signal would be given.

A system constructed in accordance with my invention has numerous advantages over burglar alarm systems generally employed in the past. It lends itself readily to the protection of either an opening or an area having no definite boundaries. It is also applicable to a room of any size in which intrusion is not desired at specified times. It is further advantageous in that no re-setting is required, since the indication of an intruder does not cause any permanent change in the elements composing the system. This is decidedly more practical than systems which depend upon the breaking or deformation of either a wire or some other object for the transmission of a signal.

My system has a further advantage in that: it is not easily tampered with as are wire networks and analogous alarm systems. As explained above, the various operating elements of the system may be placed in practically inaccessible locations and it is apparent that the antenna portion may be disguised as a metallic ceiling, a series of power 'or light wires or the like, so that the intruder would be at a loss to know just where to look for those portions of the network. A system according to my invention may be constructed and installed at a very reasonable cost and inasmuch as there are but few elements subject to deterioration, the cost of upkeep is quite low.

In addition, cutting the wire 10 as illustrated Fig. 1 or 33 shown in Fig. 2 does not break the circuit and render the device inoperative as in most other systems, but rather any tampering with the antenna will in itself give an alarn Although I have illustrated and described herein certain specific embodiments of my invention I am fully aware that many other modifications may be made and I do not intend to be limited except insofar as is neces sitated by prior art and as indicated by the following claims.

I claim as my invention:

1. In an alarm system, a balanced network analogous to a VVheat-stone bridge, a condenser, the dielectric of which comprises a space to be protected included in one arm of said network, indicating means including a demodulating device connected across points in said network between which no difference of potential exists when said network is in balance, and a source of modulated high-frequency alternating potential connected across conjugate points of said network, whereby an unbalanced condition of said network permits said alternating potential source to influence said indicating means.

2. In an alarm system, a balanced network having conjugate pairs of terminals, a demodulating device having an input circuit connected across equi-potent-ial points in said network, a source of modulated high-frequency oscillations associated with points conjugate with the points to which the demodulating device is connected, said modulation being at an audible frequency, and means for giving audible indications associated with said demodulating device, whereby an unbalanced condition of said network permits the impression of modulated high-frequency potentials on said demodulating device.

3. In an alarm system, a balanced network having conjugate pairs of terminals, a demodulating device having a tuned input circuit associated with equi-potential points in said network, a source of high frequency having a frequency commensurate with the frequency to which said input circuit is tuned, means for associating said source with points in said network conjugate with the points with which said tuned input circuit is associated, and means for modulating said oscillations at an audible frequency, whereby an unbalanced condition of said network permits the impression of modulated highfrequency oscillations on the input circuit of said demodulating device.

4. In an alarm system, a balanced network having conjugate pairs of terminals, ademodulating device having a tuned input circuit associated with equi-potential points in said network, amplifying and signal-producing means associated with said demodulating device, a source of high-frequency modulated at an audible frequency, and means for associating said source with points in said network conjugate with the points with which said demodulating device is associated, whereby an unbalanced condition of said network permits the impression of modulated high-frequency oscillations on the input circuit of said demodulating device.

In testimony whereof, I have hereunto subscribed my name this 16th day of April, 1926.

' EDWARD B. -MALLORY. 

